[jira] [Created] (MAPREDUCE-4961) Map reduce running local should also go through ShuffleConsumerPlugin for enabling different MergeManager implementations

["Jerry Chen (JIRA)" <ji...@apache.org>]

Jerry Chen created MAPREDUCE-4961:
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             Summary: Map reduce running local should also go through ShuffleConsumerPlugin for enabling different MergeManager implementations
                 Key: MAPREDUCE-4961
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4961
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
    Affects Versions: trunk
            Reporter: Jerry Chen


MAPREDUCE-4049 provide the ability for pluggable Shuffle and MAPREDUCE-4080 extends Shuffle to be able to provide different MergeManager implementations. 

While using these pluggable features, I find that when a map reduce is running locally, a RawKeyValueIterator was returned directly from a static call of Merge.merge, which break the assumption that the Shuffle may provide different merge methods although there is no copy phase for this situation.

The use case is when I am implementating a hash-based MergeManager, we don't need sort in map side, while when running the map reduce locally, the hash-based MergeManager will have no chance to be used as it goes directly to Merger.merge. This makes the pluggable Shuffle and MergeManager incomplete.

So we need to move the code calling Merger.merge from Reduce Task to ShuffleConsumerPlugin implementation, so that the Suffle implementation can decide how to do the merge and return corresponding iterator.




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